<!DOCTYPE HTML>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>计时器</title>
</head>
<script type="text/javascript">
    var num = 0, i;

    function startCount() {
        document.getElementById('count').value = num;
        num = num + 1;
        i = setTimeout("startCount()", 1000);
    }

    function stopCount() {
        clearTimeout(i);
    }
</script>
</head>
<body>
<form>
    <input type="text" id="count"/>
    <input type="button" name="start" value="开 始" onclick="startCount()"/>
    <input type="button" name="stop" value="停 止" onclick="stopCount()"/>
</form>
</body>
</html>